High performance gas turbine engines require cooling passages and cooling flows to ensure reliability and cycle life of individual components within the engine. For example, to improve fuel economy characteristics engines are being operated at higher temperatures than the material physical property limits of which the engine components are constructed. These higher temperatures, if not compensated for, erode engine components and decrease component life. Cooling passages are used to direct a flow of air to such engine components to reduce the high temperature of the components and prolong component life by limiting the temperature to a level which is consistent with material properties of such components.
Conventionally, a portion of the compressed air is bled from the engine compressor section to cool these components. Thus, the amount of air bled from the compressor section is usually limited to insure that the main portion of the air remains for engine combustion to perform useful work.
As the operating temperatures of engines are increased, to increase efficiency and power, either more cooling of critical components or better utilization of the cooling air is required.
Various arrangements for using cooling air to increase cycle life and reliability are available. U.S. Pat. No. 4,173,120 issued to William C. Grosjean et al on Nov. 6, 1979 discloses a cooling flow system. The system includes an air cooled nozzle and shroud assembly having a leading and trailing edge. An inner air reservoir is interconnected to a plurality of air flow passages which connects the reservoir with the leading edge and trailing edge internal plenum. The cooling air flows into the inner air reservoir and a portion of the cooling air internally impinges the leading edge through the plurality of passages near the leading edge and a portion of the cooling air exits along the trailing edge of the nozzle. Another portion of the cooling air from the reservoir exits the bottom portion of the nozzle below the turbine rotor blades and is further used as a buffer protecting the stator diaphragm from hot gas ingestion.
Another arrangement of using cooling air to increase cycle life and reliability is disclosed in U.S. Pat. No. 4,668,162 issued to Philip J. Cederwall et al on May 26, 1987. In this patent a cooling system includes a nozzle and shroud assembly having a plurality of through passages for transferring cooling air through the nozzle and a separate passage providing nozzle inner shroud cooling. From a reservoir below the nozzle a plurality of passages are provided for the cooling air to exit into an area below the turbine blades for buffering the hot power gas from reaching the rotor.